It is well known that bacterial infections are often made worse by concurrent viral infections, a condition known as "bacterial superinfection". Infection of the human airways by specific viruses (e.g., influenza, respiratory syncytial virus (RSV) and parainfluenza virus (PIV) have been associated with bacterial pathogens such as non-typified Haemophilus influenzae (NTHi). The airways of cystic fibrosis patients are often colonized by Pseudomonas aeruginosa at similar times that these patients are also susceptible to respiratory viruses although the association between the two pathogen-types is less well documented. Potential mechanisms proposed to result in bacterial super infection include: viral-induced alteration of innate immune systems; reduced mucociliary clearance; the accumulation of excess/altered airway secretions; and, reduced activity of phagocytotic cell-types. Evidence also exists for viral-induced up-regulation of bacterial adherence receptors on epithelial cells. We propose to use an in vitro model of human ciliated airway epithelial cells (HAE) that display many of the physiological functions of the airway epithelium in vivo to perform systematic and quantitative analyses of the effect of viral infection on bacterial superinfection. For [unreadable] these studies we have chosen RSV and PIV3 since we are confident that we can infect HAE with these [unreadable] viruses and maintain the cultures for extended periods post-inoculation. We will attempt to determine the mechanisms that are altered by these viruses that may lead to superinfection by NTHI and PA. We propose the following Specific Aims: 1) Does viral-infection of human ciliated cells promote early bacterial interactions with the airway surface microenvironment? 2) To determine the patho-physiological consequences of viral-infection of ciliated cells that result in bacterial superinfection. 3) To identify potential bacterial attachment factors that are up-regulated by viral-Infection. Elucidation of the processes/molecules that may be altered by viral infection may give insight into new therapeutic targets to limit these effects and thus reduce the pathology associated with bacterial superinfection. The novel aspect of these studies are the bringing together of methods to measure physiological and molecular changes induced by viruses in a single model system that accurately resembles the cell-type distribution of the human airway epithelium. [unreadable] [unreadable] [unreadable]